Oh, and for everyone coming here after Paulo's talk today: We missed to mention https://gitlab.com/islandoftex/archive which provides an archive of older (abandoned) TeX-related projects (hosted on SourceForge or other hosters where it is unclear whether old source code is well preserved). If there are any ideas what's missing, simply reach out to us 🙂
Ideally you wouldn't install all of TeX Live into a single layer as you are doing right now. The perfect layering would install packages with a similar update frequency in upper layers and base packages in lower layers.
Putting weekly updates in their own layer should work out. There is an upper limit of 125 layers (or so) in a Docker image, but since TeX Live releases only live for a year there can be at most 52 weekly updates.